Method and apparatus for testing wheels and defect detection in wheels

ABSTRACT

Wheel testing apparatus according to the invention comprises at least one search unit positioned &#39;&#39;&#39;&#39;in-track&#39;&#39;&#39;&#39; replacing a portion of a rail so that the gauged wheels of a passing railroad train roll thereover. Each search unit has a thin vertical rail aligned with the gauge edge of the track for supporting each passing wheel adjacent to its flange, and thereby exposing the running surface of the wheel for testing in a zone which does not interfere with the wheel&#39;&#39;s path. Each search unit has two ultrasonic transducers enclosed in a flexible fluid-filled boot and are positioned adjacent to the thin vertical rail in the test zone under the running surfaces of passing wheels, the fluid-filled boot providing good ultrasonic coupling therewith. The transducers are angled and opposed; ultrasonic energy pulses are refracted substantially tangent to the wheel and thereafter travel about the periphery of the wheel in opposite directions, depending on which transducer is pulsed. The pulse travels around the wheel and returns to the search unit, where a portion of the pulse is returned from the wheel to the second transducer confirming the presence of the pulse in the wheel and halting further pulsing of the first transducer. The returned pulse also is used to adjust the amplified gain of the output of the first transducer, which is monitored for echo pulses reflected from defects in the surface of the wheel. The travel time of pulses around the wheel is measured to indicate wheel size. A wear measurement is made by measuring the time interval between the time for the pulse to travel about the periphery of the running surface and the time for the pulse to travel about the larger diameter flange. Outputs from the electronic test circuit include a defect alarm signal, an excessive wear alarm signal, a wheel size indication, and a test certification signal. These outputs trigger pressurized color-coded paint sprays for marking the wheels if they are passing at low speed, or terminals for connection with automatic car identification systems for recording information relating to the wheels passing at either low or high speed.

XR ata trioe Cowan et al.

[ May28, 1974 l l METHOD AND APPARATUS FOR TESTING WHEELS AND DEFECT DETECTION lN WHEELS [75] Inventors: John Vincent Cowan, Danbury;

Gerald DeG. Cowan, New Preston; John Gerald Cowan, Southbury, all of Conn.

[73] Assignee: Scanning Systems, lnc., Danbury,

Conn.

[22] Filed: Nov. 17, 1971 [2l] Appl. No.: 199,487 g r 52 05.0 ..73/67.5R 51 lnt.Cl. ..G01n 2sy0 4 [58] Field of Search 73/675, 67.7, 67.87673 8,

[56] References Cited UNITED STATES PATENTS 2,439,130 4/l948 Firestone 73/67.8 3,229,508 1/1966 Sharpe et al...... 73/675 R 3,242,722 3/1966 Barr et al 73/67.8 S 3,596,503 8/1971 Gay et al. 73/673 S Primary Examiner-Richard CJQueisser Assistant Examiner-Arthur E. Korkosz I Attorney, Agent, or Firm-Mattern, Ware & Davis [57] ABSTRACT Wheel testing apparatus according to the invention comprises at least one search unit positioned intrack replacing a portion of a rail so that the gauged A wheels of a passing railroad train roll thereover. Each gauge edge of the track for supporting each passing wheel adjacent to its flange, and thereby exposing the running surface of the wheel for testing in a zone which does not interfere with the wheel's path,

Each search unit has two ultrasonic transducers enclosed in a flexible fluid-filled boot and are positioned adjacent to the thin vertical rail in the test zone under the running surfaces of passing wheels, the fluid-filled boot providing good ultrasonic coupling therewith.

The transducers are angled and opposed; ultrasonic energy pulses are refracted substantially tangent to the wheel and thereafter travel about the periphery of the wheel in opposite directions, depending on which transducer is pulsed. The pulse. travels around the wheel and returns to thesearch unit, where a portion of the pulse is returned from the wheel to the second transducer continuing the presence of the pulse in the wheel and halting further pulsing of the first transducer. The returned pulse also is used to adjust the amplified gain of the output of the first transducer, which is monitore d for echo pulses reflectEH from defects in the surface o f tlie wlieel. The tiavelitifiiefof pulses around the wheel is measured to imiicate wheel size.

Twear measurement is made by measuring the time interval between the time for the pulse to travel about the periphery of thefi riiiingsurface and the time for the pulse to travel about the larger diameter flange.

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|l||lllll|l lllllllll lull lllllllnlllllllllllllll PATENTEMM 28 1914 lIr' m 6%} wmwy METHOD AND APPARATUS FOR TESTING WHEELS AND DEFECT DETECTION IN WHEELS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to wear measurement and defect detection in wheels. More particularly, this invention relates to ultrasonic testing of metallic railroad wheels for defects and excessive wear. The testing is accomplished in-track on moving wheels.

It is well known that wheel failures due to either extreme wear or defects, such as thermal cracks, are a major cause of train derailments. Therefore, it is highly desirable to sidetrack rolling stock having defective or excessively worn wheels, and to repair or replace such wheels before the tragedy of a derailment occurs.

it is also well known that tire failures in vehicles such as trucks, busses, automobiles and aircraft are a cause of serious accidents, resulting in great personal injury and property damage. Effective methods and apparatus for regularly and accurately testing tires are, therefore, also very desirable.

2. Prior Art No satisfactory automated means capable of testing railroad wheels on rolling stock for wear or defects presently exists. Defective railway wheels are currently located by trained inspectors who visually check for cracks in the running surface, flange and plate sections of each wheel when it is stationary in a railway yard. Though many defective wheels are found in this manner, many more escape detection due to other equiprnent. such as brake shoes, journal boxes, etc., obscuring the inspectors field of view. Also, small or subsurface defects are difficult for an inspector to find. Measurement of wheel wear is also performed at such times by physical placement of a gauge which measures the height ofthe flange above the running surface of wheel, an altogether inefficient process.

Magnetic testing of locomotive wheels has also been performed by mounting small detector coils on the locomotive in close proximity to the wheels. Small cracks. such as thermal cracks, which may develop when the locomotive is in motion disrupt the magnetic field, thereby triggering an alarm signal. This method of testing wheels is impractical because of the expense and difficulty of installing and maintaining magnetic testing apparatus at each wheel on each railway car. Furthermore, no provision for measurement of wheel wear is made in such devices.

more extensively all require that wheels and axle sets be removed from the railroad car for testing. These means include inspection of wheels by ultrasonic Contact or by magnetic particle inspections. Although these inspection methods are quite effective, it is not feasible to regularly remove every wheel from a railroad company's entire rolling stock. Furthermore, freight trains are usually assembled at marshalling yards or division points, from cars owned by different railroad companies. It is desirable for an individual railroad company to quickly and accurately examine the wheels of such cars before including them in a train. Yet, it would be totally impractical to thoroughly check the wheels of each car by presently known methods when assembling a freight train, and visual inspection alone is too time consuming and inaccurate to suffice.

Railway cars or locomotives whose wheels are found to be defective or excessively worn are removed from service. Depending on the nature of the defect or wear, wheels or axle sets of wheels are replaced, or in some cases the vehicle is sent to a wheel truing machine to re-establish a correct wheel profile.

Similarly, no automated means for testing tires of trucks, busses, automobiles, and aircraft is currently available. Detection of defective tires is limited to visual inspection, and such inspection often does not disclose damage to the tire casing, including breaks in the reinforcing tire cord.

SUMMARY OF THE lNVENTlON An object of the invention is to provide economical and highly effective methods and apparatus for the detection of defects in wheels.

Another object of the-invention is to provide methods and apparatus to detect excessive wear of wheels.

A further object of the invention is to provide methods and apparatus for testing wheels for defects and wear, and to certify that testing has been performed.

An additional object of the invention is to provide methods and apparatus for testing for defects and wear in railroad wheels mounted on moving cars and locomotives.

A still further object of the invention is to provide methods and apparatus for testing railroad wheels for defects and wear without disrupting the usual and normal marshalling of railroad cars and patterns of train movement.

Wheel testing apparatus according to the invention comprises at least one search unit positioned intrack" replacing a cut away portion of a rail. The search unit has a thin vertical rail positioned in the removed portion of rail and aligned with the gauge edge of the remaining rail. thereby providing support for passing railroad wheels. The thin vertical rail supports a wheel rolling thereover adjacent to its flange, and thereby exposes most of the running surface of the passing wheel to a test zone in the cutaway portion of the rail adjacent to the thin vertical rail positioned therein. Test equipment positioned in this zone does not alter or intrude into the normal path of the wheel.

Each search unit has two tungsten-filled, urethanecasing-backed transducers mounted in a lightweight microballoon-filled shielding mask supported in an upwardly springed-biased parallel-axis gimbal suspension system. The transducers, mask, and gimbal suspension system are enclosed in a flexible fluid-filled boot and are positioned adjacent to the thin vertical rail in the test zone, the fluid-filled boot provides a good accousting path from the transducer to the running surfaces of passing wheels. Two positioning arms upstanding from the gimbal suspension system engage the running surface of each passing wheel and align the longitudinal axes of the transducers with the running surface, maximizing delivery of ultrasonic energy thereto.

One of the transducers is held in the mask with its sonic axis inclined with respect to a plane tangent to the running surface of the wheel positioned on the search unit. The angle of inclination is determined by Snell's Law. Ultrasonic energy pulses delivered along the sonic axis into the wheel are refracted substantially tangent to the wheel and thereafter travel about its periphery in a first direction. The second transducer, also held in the mask, is opposed to the first transducer, i.e., with its sonic axis also inclined with respect to the running surface wherein pulses produced by the second transducer are delivered into the wheel and refracted substantially tangent thereto, and travel about the wheel's periphery in the opposite direction.

The ultrasonic energy pulses used for testing herein have a relatively low frequency below 1,000 KHz, and preferably 400 KHz. These pulses achieve a deep penetration of ultrasonic energy into the wheel. The ultrasonic energy pulse tends to migrate toward the surface of the wheel as it travels thereabout concentrating a surface wave component immediately adjacent to the running surface. A portion of the wave also migrates .to the larger diameter flange of the wheel and travels thereabout.

Positioning of the transducer in the mask as described above causes a portion of the pulse circling the wheel and passing the boot-wheel interface to be refracted through the coupling fluid in the boot to impinge upon the transducer opposed to the sending transducer. A defect in the running surface of the wheel causes a portion of the pulse to be reflected back along the periphery ofthe'wheel as a defect echo pulse. A portion of that defect echo pulse is refracted out of the wheel at the boot-wheel interface to impinge upon the sending transducer. indicating the presence ofa defeet.

As a wheel approaches the search unit, the transducer facing the direction of approach is repetitively pulsed at an interval greater than the time necessary for the pulse to travel about the largest diameter wheel to be tested. When the wheel contacts the search unit, an ultrasonic energy pulse is introduced into the running surface thereof, and travels about the wheel to return to the boot-wheel interface, whereat a portion of the pulse is returned from the wheel to the second transducer. This confirms the presence of the pulse in the wheel and halts further pulsing of the first transducer.

able strength. The travel time of the pulses about the periphery of the wheel is measured to indicate the wheel size.

After substantial attenuation of the first pulse in the wheel, the functions of the two transducers are reversed, and the wheel is further tested by pulsing the second transducer to produce an ultrasonic energypulse traveling about the periphery of the wheel in the opposite direction. The second transducer is preferably pulsed in synchronism with the attenuating throughtransmission pulses remaining in the wheel. The sending transducer is monitored for defect echo pulses. A wear measurement is made by measuring the time interval between the time for the pulse to travel about the periphery of the running surface and the time for the pulse to travel about the larger diameter flange.

For testing wheels moving at high speeds wherein the wheel passes the search unit prior to delivery of the second pulse, a second. closely spaced parallel operating search unit is provided. Testing in the second direction is accomplished as the wheel passes thereover.

The wheel testing apparatus further comprises gauging means for gauging approaching wheels, switch means sensing the direction of approach of wheels, coupling fluid spray means for wetting the surface of the flexible boot for better ultrasonic coupling at the boot-wheel interface, and an electonic test circuit for operating the transducers in the above-described manner. A unique feature of the test circuit comprises getting all through-transmission pulses into one channel and all defect echo pulses into a second channel so that the amount of circuitry is minimized. Outputs from the electronic test circuit include a defect alarm signal, an excessive wear alarm signal, a wheel size indication, and a test certification signal. These outputs trigger pressurized color-coded paint sprays for marking the wheels if they are passing at low speed, or terminals for connection with automatic car identification systems for recording information relating to wheels passing at either low or high speed A second wheel testing apparatus is preferably installed in the opposite rail of the track for testing remaining wheels on the other side of the train.

THE DRAWINGS FIG. 1 is a perspective view of a search unit according to the invention mounted in a rail for testing an approaching wheel.

FIG. 2 is a side elevation view of the search unit of FIG. I and the associated supporting structure.

FIG. 3 is a top plan schematic view of wheel testing apparatus for both low and high speed testing.

FIG. 4 is an exploded perspective view of a portion of the search unit of FIG. I, including a spring-biased parallel-axis gimbaled suspension mounting means for a transducer-carrying mask.

FIG. 5 is a vertical cross-sectional view of the search unit of FIG. 1, taken along the lines 5-5 of FIG. 2.

FIG. 6 is a similar vertical cross-sectional view of the search unit, showing the parallel axis gimbaled suspension conforming to a railroad wheel.

FIG. 7 is a similar vertical cross-sectional view of the search unit, showing the gimbaled suspension conforming to a worn railroad wheel.

FIG. 8 is a vertical side cross-sectional view of a portion of the gimbaled suspension means and the transducer carrying mask having two transducers mounted therein, with a wheel positioned for testing.

FIG. 9 is a schematic side elevation view of a wheel positioned over a search unit for defect testing.

FIG. 10 is a timing diagram indicating the operation of the two transducers of FIG. 9.

' FIG. 11 is a similar schematic view of a wheel positioned on a search unit for testing.

FIG. 12 is a timing diagram indicating the operation of the transducers of FIG. 11.

FIG. 13 is a similar schematic view of a wheel moving across two search units for high speed testing.

FIG. 14 is a timing diagram indicating the operation of the transducers of FIG. 13.

FIG. 15 is a similar schematic view of a wheel posltioned on a search unit for wear testing.

FIG. 16 is a timing diagram indicating the operation of the two transducers of FIG. 15.

FIG. 17 illustrates the placement of FIGS l7A-E to comprise an electrical circuit diagram.

FIGS. 17A-E are portions of an electrical circuit diagram comprising FIG. 17.

FIG. 18 illustrates the placement of FIGS. l8A-B to comprise a timing diagram of the operation of the electrical circuit shown in FIG. 17.

FIGS. ISA-B are portions of the timing diagram of FIG. 18.

The same members refer to the same. elements throughout the various figures.

PREFERRED EMBODIMENT Two wear measurement and defect detection systems adapted for testing railroad wheels on moving trains are shown in FIG. 3. A first test system generally indicated at l, is particularly adapted for testing wheels moving at relatively low speeds of less than 30 mph, and usually at speeds of 5-10 mph. such as are encountered in hump yards or marshalling yards. The test system 1 generally comprises a search unit 120 positioned intrack, as shown in FIG. 1. The search unit 12a houses two ultrasonic transducers in a shielding mask which is mounted in a spring-biased parallel-axis gimbal suspension system for aligning the transducers with the running surface 38 of wheel 40, wherein the transducers can introduce an ultrasonic energy pulse into the wheel and monitor ultrasonic energy pulses returning from the wheel, as will be more fully described below.

Referring again to FIG. 3, search unit 120 is connected by coaxial cables 17 with an electronic test circuit 20a having a direction control portion 21, a pulse control portion 22, an automatic gain control portion 23, a test certification portion 24, a defect test portion 26, a wear measurement portion 28, and a wheel size indicator portion 29. Connected to the electronic test circuit 20a is a support unit 30a containing a power supply 32, a main sync generator 34, and a video display 36.

As a wheel 40 approaches search unit 12a from the left in FIG. 3, it is engaged by a gauging device 42 which consists of a C-shaped metal member approximately -15 feet long mounted adjacent to and spring biased toward the inside or gauge side of rail 2. The gauging device 42 positions the running surface 38 of wheel 40 centrally on top of rail 2 by engaging flange 39 of the wheel and urging the flange into contact with the inside of the rail. It is desirable to have the running surface positioned in this manner for testing.

After being gauged" the wheel 40 next contacts a switch 430 which indicates to the electronic test circuit a the direction from which the wheel is approaching. Contact with switch 43a also causes operation ofa coupling fluid spray dispenser 44a.

As the wheel passes over search unit 120 it is tested.

' The test certification portion 24 of the electronic test circuit 20a determines if testing of the wheel has been accomplished, and triggers a pressurized certification paint spray dispenser 48 to provide a visual record thereof on the wheel.

If a defect is discovered by the test, the defect test portion 26 of the electronic test circuit triggers operation ofa defect paint spray dispenser 50 to mark the defective wheel. Similarly, the wear measurement portion 28 of the electronic test circuit 20a causes an excessive wear paint spray dispenser 52 to mark the worn wheel. The wheel size indicator portion 29 of the electronic test circuit provides an output on one of terminals 621,

Referring still to FIG. 3, the wheel 40 next passes over a switch 540 indicating that the wheel has passed the search unit 12a.

If wheel 40 were approaching search unit 12a from the opposite or right hand direction, the wheel would be first gauged by a gauging device 56, and pass over switch 54a indicating to the direction control portion 21 of the electronic test circuit 20a that the wheel is approaching from the left. The coupling fluid spray dispenser 440 would also be activated.

To test wheels on the opposite side of the train, a second wheel testing system similar to system 1 described tested is indicated.

above would be positioned in the opposite rail 11. The distance between such a second test system and system 1 would preferably be in excess of feet. This distance is necessary because the wheels of the train are to be gauged against the inside of rail 11, and therefore the two gauging units are working in opposition on a very heavy mass. If the test systems including the gauging devices are located too closely together, proper gauging will not occur.

A wear measurement and defect detection system 10 adapted for testing wheels of trains moving at relatively high speeds up to mph. is also shown in FIG. 3. The system 10 generally comprises two search units 12 and 13, each positioned in-track" in rail 11, the two search units being separated by not more than 3 feet. The 3 foot limitation on separation of the search units is desirable because the axle centers on some tandem wheel cars are 6 feet or less apart. and wider separation of the search units could therefore result in confusion as to the particular wheel being tested.

Search units 12 and 13 are connected by coaxial cables 19 to a second electronic test circuit 20 and associated support circuitry 30. The electronic test circuit 20 is identical to test circuit 200 used for the low speed test system 1, except that an output terminal 656 is provided for the test certification system, an output terminal 640 is provided for the wear alarm from the wear measurement portion, and an output terminal 575 is provided for an alarm signal from the defect test portion. These output terminals may be connected to an automatic car identification system or hot box detector read-out wherein a written record of wheels tested or wheels needing replacement or repair can be provided.

The high speed test system 10 also tests wheels moving at low speeds, and paint spray dispensers could be provided to mark slowly moving wheels. However, paint spray dispensers are not practical to mark wheels moving at high speeds.

As a wheel 40 approaches search units 12 and 13 from the left in FIG. 3, it is engaged by a first gauging device 14 and subsequently by a second gauging device 15, both similar to gauging device 42 described above. The gauging devices operate to urge the flange of the wheel into contact with the inside rail 11, and two gauging devices are necessary because of the high speed of the train. The gauging devices may be separated by approximately 20 feet. The separation between gauging device 15 and the search unit 13 may also be about 20 feet.

As the wheel approaches search unit 13 it passes over a switch 54 indicating to the electronic test circuit the direction of approach of the wheel, and operation of coupling fluid spray dispensers 44 and 46 are thereby triggered. The wheel passes over search units 12 and 13 for testing, and then operates switch 43 which signals the electronic test circuit that the wheel has passed.

1f the wheel 40 were approaching from the right in FIG. 3, it would similarly be gauged by a first gauging device (not shown) and a second gauging device 16, and subsequently pass over the switch 43 indicating the direction of approach and triggering operation of the coupling fluid spray units 44 and 46. Gauging device 16 may also be positioned approximately 2.0 feet from search unit 12.

Testing of the wheels on the opposite side of a high speed train is accomplished by providing a similar test system positioned in the opposite rail. The two test systems are positioned so that there is approximately 200 feet between the opposite-acting gauging devices, melymiiiimiiimgfh pfoblem of regau ging wheel and axle sets against the opposite rail.

Search Unit The search units 12-13 comprise the interface between the electronic test circuit and the railroad wheel being tested. They also comprise a rail adapted for supporting passing wheels wherein many tests can be performed.

Referring now to H0. 1, a portion of the rail 11 is cut away, and search unit 12 is mounted in the resulting space. The search unit 12 comprises first a flat base plate 100 having upstanding therefrom two vertical flanges 102 and 104 disposed generally transverse to rail 11. The base plate and the upstanding flanges are cast of strongly ribbed nickel alloy steel.

A thin sturdy rail 106 is seated on the base plate 100 at 108 and is further attached to the base by bolts threaded into flanges 102 and 104. The thin rail 106 has a curved top surface 110 which bridges the gap in rail 11 and provides a support adjacent to the flange of wheels passing over the search unit. Thus, the running surface 38 of wheel 40 is exposed to a test zone comprising the cutaway portion of rail 11. Various test equipment could be positioned in this zone, and testing on passing wheels can be accomplished without disruption of normal railway trafiic.

Because of the great weight carried by rail 106, it is preferably fabricated of air-hardened tool steel, heat treated to 54-58 Rc for maximum wear and strength characteristics, and chemically treated for minimum deterioration from corrosion. 1f the rail 106 is damaged or becomes worn during use, it can readily be replaced at the in-track installation in a matter of minutes.

The base plate 100 is positioned on a concrete foundation 112 which replaces the usual railroad ties below the cutout portion of rail 11. Referring now to H0. 2, the concrete foundation 112 is formed around a steel l-beam 114 which carries ties 116-119 supporting rail 11 adjacent to search unit 12, and the ends of rail 11 immediately adjacent to the search unit 12 rest on the concrete foundation 112 at 120 and 121. The concrete foundation 112 and the l-beam 114 therefore support each rail 11 and the thin rail plate 106 of search unit 12 together, providing a smooth running surface for wheel 40 as it approaches and travels over search unit 12.

TRANSDUCERS AND MASK The search unit '12 incorporates two rectangular transducers 122 and 124 which are mounted in a transducer mask 126, as best seen in FIGS. 4 and'8. The desired frequency for testing railroad wheels is in the range of 200 to 1,000 K112, and the preferred frequency is approximately 400K112.

The transducers comprise rectangular lead zirconate piezo-electric crystals having a positive silver electrode plated on top surfaces 123 and and a negative silver electrode plated on bottom surfaces 128 and 129. The active area of the electrodes is approximately 2 inches by inch, and the transducers are pulsed with 20 amperes of current at 1,500 volts to produce 400 KHz ultrasonic energy pulses.

The top positive silver electrode is electrically insulated by molding thereon a urethane coating 127. This coating is virtually transparent to ultrasonic energy wavesin the frequency range of 200 to 1,000 KHz, and therefore does not interfere with the transmitting and receiving capability of the transducer.

The directional radiating capability of the transducers 122 and 124 is enhanced by embedding their respective rear faces 128 and 1 29 in a tungsten-particlefilled elastomer casing 130. The casing has a substantially semi-circular cross section, and extends the axial length of each transducer. It is heavy. and damps" wave fronts emanating from the rear faces of the transducer. and also actually inhibits displacement of the rear faces. Consequently, upon pulsing the transducers the exposed front faces 123 and 125 achieve a greater displacement and thereby transmit stronger wave fronts. The receiving capabilities of transducers 122 and 124 are similarly enhanced by the casing 130.

The transducer mask 126 matingly receives the two transducers 122 and 124 and their tungsten-filled elastomer casing 130 in two elongated transverse semicircular sockets 138 and 139. The two transducers are axially aligned and their front surfaces 123 and 125 are tilted toward each other. The sonic axes 132 and 134, normal to the front faces of the transducers, are each disposed at an angle from vertical axis 136 in the range of 28 to 42, and preferably 35 as shown at 133 and 135 in FIG. 8.

The mask 126 functions to minimize unwanted interaction between the two transducers 122 and 124, and to direct pulses emanating therefrom toward wheel 40, shown directly over search unit 12. Also, the mask functions to direct ultrasonic energy pulses returned from wheel 40 to impinge on the transducer faces. Accordingly, the mask 126 comprises a central stem positioned between the two sockets 138 and 139 wherein direct communication from radial mode cross-talk between the two transducers is minimized. The mask further comprises two wave-guide flanges 142 and 144 flanking the two transducers. Wave-guide flange 142 and the central stem 140 combine to provide a channel opening defined by planes 146 and 148 for directing ultrasonic energy pulses between transducer 122 and zone 149 on wheel 40 passing over the search unit. Similarly, wave-guide flange 144 and central stem 140 combine to form a second channelopening defined by planes 151 and 153 extending between transducer 124 and a second zone 154 on wheel 40.

The mask is preferably fabricated of urethane filled with micro-balloons." Micro-balloons are nitrogen filled spheres having phenolic outer casings with diameters in the range of 0.001 to 0.004 inches. The proportion of micro-balloons to urethane may be in the range of lto 18 by weight, and is preferably l to 6 by weight. The micro-balloon filled urethane exhibits very good attenuating characteristics for ultrasonic energy in the frequency range below 1,000 K112, and is also very light in weight.

Referring now to FIGS. 4 and 5, the mask 126 has two circular bosses 156 and 157 raised from sidewall 158 and forming the ends of sockets 138 and 139. Two similar circular bosses 160 protrude from the opposing sidewall 162, and those bosses have a semi-circular central portion cut away to provide access to sockets 138 and 139 for slidingly mounting the transducers and their tungsten-filled urethane casing. The electrical leads 131 and 137 for transducers 122 and 124 also pass through the semi-circular openings, and are connected to co-axial fittings 70 and 71 on side plate 200.

Sidewall 158 extends upward from the body of mask 126 and terminates at its upper portion in a flange 164 having a vertical slot 166 formed therethrough. Sidewall 162 similarly terminates in an upper flange 168 also having a vertical slot 169 formed therethrough.

PARALLEL AXIS-GIMBAL SUSPENSION The search unit 12 further comprises a spring-biased, parallel-axis gimbal suspension means for positioning the two ultrasonic transducers 122 and 124 and mask 126 in proper orientation for transfer of ultrasonic energy pulses to and from the wheel being tested. Accordingly, the search unit 12 next comprises a side plate 200 which is removably secured to flanges 102 and 104 by means of-bolts 202 and 204 (See FIG. 1). Referring now to FIGS. 4 and S, a spring-biased parallel-axis gimbal suspension means 210 attached to the inside of side plate 200 carries the transducer mask 126 in which the transducers 122 and 124 are housed.

The gimbal suspension means 210 consists of a first pivot shaft 212 carried in two C-shaped cradles 214 attached to the inside of side plate 200. At each end of pivot shaft 212 are secured arms 216 extending outward from near housing plate 200 to a second pivot axis comprised of two individual pivot shafts 218. The axis of shafts 218 is parallel to the axis of first pivot shaft 212.

The pivot shafts 218 pass through the end walls 220 of a rectangular metal housing 221 adapted to engage and carry the mask 126, and the shafts are secured thereto by flanking bushings 222. A first side wall 224 of the rectangular housing 221 joins the two end walls 220 adjacent to side plate 200 and pivot shaft 212. The side wall 224 has formed therein two round openings 226 and 227 which are adapted to engagingly receive the two circular bosses 160 on side 162 of mask 126. The sidewall 224 has an upwardly-protruding positioning arm 228 which extends through slot 169 in mask 126. i

The mask 126 is mounted in the housing 221 by first inserting positioning arm 228 into slot 169. and subsequently attaching a second housing having sidewall 230 by inserting its corresponding positioning arm 232 through slot 166 in mask 126 and engaging the circular bosses I56 and 157 in the openings 234 and 235. The mask is secured in the gimbal suspension means by firmly attaching the second housing sidewall 230 to the endwalls 220 by means of screws.

The tips of positioning arms 228 and 232 are covered by caps 238 and 239. The tops of the caps are slightly arched. and the caps are fabricated of a smooth. long wearing material such as urethane. The caps protect a urethane boot 250 from being punctured by the positioning arms.

The gimbal suspension means is biased upward to present the two positioning arms 228 and 232 to the running surface 38 of the wheel being tested. Referring to FIGS. 4-7, a coil spring 240 is coiled above pivot shaft 212. One end of the coil spring extends downwardly from the shaft 212 and seats against the side plate 200 at 242. The other end 243 of spring 240 extends outward from the pivot shaft 212 and is engaged under the arm 216. Thus the tension in coil spring 240 pivots arm 216 upward and lifts the positioning arm 232 upward against the running surface of a passing wheel. (See FIGS. 6 and 7). Another similar spring 240a may also be provided on pivot shaft 212.

A second coil spring 245 is secured to the side plate 200 at 246 and is attached to the bottom edge of the inside housing plate 224 at 247. The tension in spring 245 lifts the inside housing plate, thereby urging positioning arm 228 upward against the running surface of the passing wheel. When both positioning arms contact the running surface of the wheel, optimum alignment of the transducers and the running surface is achieved.

The parallel-axis gimbal suspension means 210 and the mask mounted therein are completely surrounded by a urethane boot 250, best seen in FIGS. 1, 5 and 8. The boot 250 is similar to a bag, having one open end which is positioned adjacent to the housing plate 200 and secured thereto by means of a retaining flange 252 which interlocks with a peripheral lip 255 of the boot. The peripheral flange 252 is secured to side plate 200 by means of recessed machine screws 254 passing through the side plate 200 into the flange 252, wherein the boot 250 may be easily changed if it becomes worn or damaged.

The boot is filled with a coupling fluid 260 which efficiently transmits ultrasonic waves. This fluid is preferably a 1:1 mixture of water and ethylene glycol, which resists freezing in cold temperatures. The boot is filled by means ofa first check valve 262 (See FIG. 1) for introducing fluid through the side plate 200. A second check valve 264 is connected by tubing 265 to cap 238 on the top of positioning arm 228, whereby air may be vented from the top portions of the boot 250 as the boot is being filled.

The gimbal suspension means, the mask, and the transducers, all enclosed by boot 250, are mounted on side plate 200. Therefore, these parts can be quickly removed, and replaced as a unit, and testing can be continued with little "down time in case of search unit failure.

Referring now to FIG. 6, the railroad wheel 40 having an unworn running surface 38 is shown passing over the Search unit 12. The wheel is supported adjacent to flange 39 on the top surface of the thin rail 106,

whereby most of the running surface 38 is available for coupling with boot 250 or other test equipment. The flange 39 is always closely positioned against thin rail 106 because the gauging devices such as 42 urge the flange against the inside or gauge edge of the track. The running surface of an unworm railroad wheel has a slight pitch with respect to the horizontal, the pitch being approximately one-twenty, the pitch being exaggerated in FIG. 6 for purposes of illustration.

The capped tips of positioning arms 228 and 232 are respectively urged upwardly against the running surface 38 by means of springs 240 and 245. Thus, the two positioning arms and the parallel-axis gimbal mounting means serve to hold the mask and associated transducers with the longitudinal axis of the transducers parallel to the wheels running surface. This maximizes the exchange of ultrasonic energy pulses between the transducers and the wheels, and properly directs the waves in relation to the wheel, as will be more fully discussed below.

Also shown schematically in FIG. 6 is a shock absorber 85 mounted between bottom of boot 250 and the bottom of mask 126. The shock absorber is helpful during high speed testing when wheel-search unit contact may bounce the mask. The light weight micro-balloon filled urethane material produces a low mass mask, which is also helpful in minimizing bounce."

Referring now to FIG. 7, a railroad wheel having a somewhat concave worn running surface is shown passing over the search unit. The worn running surface engages the capped tips of positioning arms 228 and 232 through boot 250, causing the transducer-mask assembly to pivot on its parallel-axis gimbal suspension means and to align the longitudinal axis of the transducers parallel to a central tangent to the worn running surface.

The fluid in the urethane boot 250 is displaced downwardly as the wheel rolls over the search unit, depressing boot 250. As the fluid is essentially incompressible,

the boot is caused to closely conform to the running surface of the wheel, and, referring to FIG. 8, to cause the boot to wrap about a portion of the wheels periphery encompassing zones 149 and 154.

The interface between the outside of boot 250 and the running surface 38 of the wheel is enhanced by means ofwetting the top surface of the boot. This is accomplished by a coupling fluid spray system 44 which comprises a pressurized fluid reservoir connected to tubes 190 and 192 disposed transversely across the ends of search unit 12 (See FIG. 1). A portion of the connecting passage to tubes 190 and 192 is an internal bored passage 195 in side plate 200.

The transverse tubes 190 and 192 have a plurality of spray nozzles 193 aimed across the top surface of boot 250, and the coupling fluid spray is dispensed when the approach of the wheel is sensed by switches 43 or 54. The coupling fluid may be water, when warm tempera ture prevails, and an anti-freeze mixture in cold temperatures.

ULTRASONIC ENERGY PULSE: SHAPE, REFRACTION. AND MIGRATION Referring now to FIG. 8 wherein wheel 40 is positioned above the mask I26 and transducer 122 and 124 as described above, pulsing transducer 124 causes an ultrasonic energy pulse to be delivered to wheel 40. The ultrasonic energy pulse on entering wheel 40 is bent or deflected toward the left along the periphery of wheel running surface 38, travelling through a region whose boundary, in effect, is believed to have a shape substantially as outlined by dotted line 170 and the wheel running surface 38. The precise composition of the ultrasonic energy pulse in the wheel is unknown, but it is believed to have a deep surface wave component travelling through the region outlined by dotted line 172 and running surface 38, the remaining portion of the wave between dotted lines and 172 comprising shear waves refracted to travel generally about the periphery of the wheel.

Through localized probe monitoring it has been found that the high energy, low frequency 400 KHZ energy pulse attains very great penetration in the wheel 40, the initial depth of penetration D being 8 or more inches. Also, the pulse is dispersed throughout the width of the wheel, as indicated by dotted lines 174 and 175 in FIG. 6. The depth of penetration and dispersion are very useful in testing wheels and particularly railraod wheels, and would not be obtained by using ultrasonic energy pulses having frequencies well above 1,000 KHz as taught in the prior art. Such pulses would comprise a very shallow surface wave component if in,- troduced into the wheel in the manner described herein.

The ultrasonic energy pulse is caused to travel about the periphery of the wheel because of refraction. The refractive index of the fluid trapped within the boot and interposed between the transducers and the wheel is approximately I50 and the refractive index of a steel railroad wheel is approximately 2.74. The urethane boot 250 is virtually transparent to 400 KHz pulses, and is not a factor. Therefore, the wave front of the ultrasonic energy pulse presented to the railroad wheel at an angle of approximately 35 from the vertical is generally refracted approximately tangent to the surface of the railroad wheel according to Snells Law, which states:

wherein V, is the surface wave velocity in steel and V is the longitudinal wave velocity in the ethylene glycolwater mixture. Therefore, at least a portion of the ultrasonic energy pulse introduced into the railroad wheel is refracted to form a surface or Rayleigh wave front.

At the preferred frequencies the angle of incidence to the railroad wheel is not sharply critical, and pulses introduced at angles of 20 to 42 from the vertical will be refracted to have a surface wave component. The angle of 35 is preferred to give a strong surface wave component.

Although ultrasonic energy pulses normally display a tendency to travel in a straight line, the ultrasonic energy pulse in the wheel cannot escape at the steel running surface-air interface, and is therefore apparently bent to travel around the periphery of the wheel. However, the tendency of the ultrasonic energy pulse to travel in a straight line is believed to cause the portion of the ultrasonic energy pulse which has initially penetrated into the wheel to a substantial depth to gradually approach, or migrate" toward the curved running surface, thereby increasing the strength of the surface wave immediately adjacent thereto.

The migration of the surface wave toward running surface 38 is illustrated in FIG. 8. Dotted line 178 indi cates the depth of the wave after its first trip around the wheel, dotted line 179 indicates the depth after a second round trip, and dotted line 180 indicates the depth after a third round trip.

The migration phenomenon is very important for testing curved surface for surface defects because the gradual "concentration" or increase in the strength of the surface wave immediately adjacent to the surface from migration more than compensates for the attenua- Therefore, useful information can be obtained for as many as to round trips of the ultrasonic energy pulse in the wheel, whereas, considering only attenuation. useful information would only be expected for one to two round trips.

The migration phenomenon is also important for testing railroad wheels in that a portion of the ultrasonic energy pulse migrates outward to travel about the periphery of the flange of the railroad wheel, providing an opportunity for a wear measurement as will be described below.

On each round trip, a portion ofthe ultrasonic energy pulse is refracted out of the wheel at zone 149 to impinge on transducer 122. Because of the wide dispersion of the ultrasonic energy pulse, a portion of the pulse travelling about the flange 39 also impinges on transducer 122 on each round trip.

METHOD OF TESTING Referring now to FIG. 3, as wheel 40 approaches search unit 12, it operates a switch signaling to the electronic test circuit both the presence of a wheel and its direction of approach. Thereafter, the pulse control portion of the electronic test circuit repetitiously pulses the search unit transducer facing the direction of wheel approach, so that a pulse is introduced to the wheel shortly after the wheels initial contact with the search unit. Referring now to FIG. 8, transducer 124 is regu larly pulsed as wheel 40 approaches the search unit 12 from the left. The wheel first reaches the zone 154, and an ultrasonic energy pulse from transducer 124 contacts the wheel at that zone, and enters the wheel as described above.

The initial transducer pulse rate is dependent upon the types of wheels to be tested, and is particularly dependent upon the density or refractive index and the circumference thereof. For purposes of testing the wheel. it is desirable to have only one pulse in the wheel at any given time. Referring still to FIG. 8, confirmation that a pulse has entered the wheel at zone 154 occurs when the pulse has traveled completely about the periphery of the wheel returning to the wheel-boot interface, wherein a portion of the wave is refracted out of the wheel at zone 149 and impinges upon transducer 122. To assure that transducer 124 does not introduce a second pulse into the wheel, the pulsing rate of transducer 124 is set sufficiently low so that the time interval between pulses is greater than that necessary for a pulse to travel completely around the wheel. The first pulse entering the wheel at 154, traveling clockwise there around and exiting at 149. to impinge on transducer 122 produces an electrical signal which is used to inhibit further pulsing of transducer 124.

Referring now to FIG. 9, there is schematically shown wheel 40 positioned over search unit 12 having a transducer A corresponding to transducer 122 in FIG. 8 and transducer B corresponding to transducer 124 in FIG. 8. The wheel-boot interface encompassing zones 149 and 154 is designated at E. FIG. 10 is a timing diagram showing operation of transducers A and B during the test wheel 40.

Because wheel 40 is traveling from left to right, transducer B is repetitiously pulsed as indicated at 310, 311, and 312. in FIG. [0. Pulse 312 is refracted into wheel 40 and travels about the periphery thereof returning to interface E wherein a portion of the wave is refracted out of the wheel and received by transducer A as pulse 314. Referring to the scale markings, throughtransmission pulse 314 is received at A prior to the next, repetitious pulsing of transducer B indicated in dotted lines at 316, which pulse is inhibited by the pulse control upon receiving the first through-transmission 314.

Through-transmission pulse 314 comprises only a portion of the pulse passing clockwise about wheel 40. On the pulses next passage through interface zone E, an additional portion is refracted toward transducer A and received there as pulse 318. Subsequent revolu-v tenuation is apparent in the pulses received at transducer A. As noted above the attenuation is partially offset by the migration phenomenon.

The wheel 40 shown in FIG. 9 has a defect located at C. A portion of the initial clockwise traveling pulse 312 introduced into the wheel from the transducer B is reflected from the defect C back along the path C-E, wherein a portion of the reflected pulse is returned to transducer 13, as indicated at 325 in FIG. 10. As pulse 312 continues to pass clockwise around wheel 40, a further portion thereof is reflected back from defect C each time the pulse is presented thereto. The subsequent defect echoes received by transducer B are indicated at 326-330.

Despite the attenuation of the initial pulse 312 as indicated by the steady decrease of the strength of the through-transmissions 314 through 323, the size of the reflected return pulses from defect C increases and reaches its largest magnitude in the second and third reflection. Thus, pulses 326 and 327 of Fig. 10 are the largest defect echo pulses, and pulses 329 and 330 represent a decrease in reflected pulse. This phenomenon has two possible explanations. First, it is believed that as the pulse travels about the periphery of the wheel, the strength of the pulse becomes increasingly concen trated very near the surface thereof. This is because the pulse is continually being bent in a circular path, wherein the pulse would travel in a straight line if free to do so. The greater magnitude ofecho pulses 326 and 327 may then be explained because the defect C is normally of a very shallow depth, wherein a great portion of the earlier deeper pulses passing the defect would merely pass thereover. This increased strength of the echo pulses thereby provides confirmation of the migration effect described above. The position of the defect C causes the best display of this penenomenon because of the relatively short in-steel" paths between the defect and the transducer, wherein attenuation is a lesser factor.

A second possible explanation for the increased size of the third and fourth echo pulses 327 and 328 is that the first echo pulse 325 continues to rotate counterclockwise about the wheel 40. On its second passage along the arc C-E, the echo pulse would reinforce subsequent reflections of the initial clockwise traveling pulse from defect C. This second theory is believed to be less likely.

Complete testing of the wheel comprises initiating a second initial pulse in a counterclockwise direction. The second counterclockwise rotating pulse would not be useful for test purposes until the first clockwise rotating pulse has dissipated so that no confusion be- 

1. The method of inspecting a body for defects in a curved peripheral surface thereof forming an uninflected closed curve comprising the steps of: A. coupling a zone of the curved surface with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the body; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of ultrasonic energy pulses projected by the transducer being inclined with respect to a tangent plane of the zone at an angle whereby low frequency ultrasonic energy delivered to the body along the sonic axis enters the body, penetrates to a substantial depth therein, and is refracted substantially tangent to the curved surface; and whereby the energy which penetrates the body to a substantial depth travels along a path near to and converging toward the curved surface and having a progressively increasing radius of curvature, and thereby migrates toward the curved surface thereof, as it travels along said path; C. pulsing the first ultrasonic transducer to produce a low frequency ultrasonic energy pulse; and D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the curved surface and refracted out of the body at the coupled zone to impinge on the first ultrasonic transducer.
 2. positioned to span the longitudinal distance between the adjacent ends of the first and second rail segments,
 2. switch the output of the first transducer to the defect signal detector, and
 2. The method of inspecting a body for defects in a curved peripheral surface thereof as defined in claim 1 wherein the curved uninflected peripheral surface comprises a convexly closed path and monitoring the first ultrasonic transducer for echo pulses is continuously performed during the time period that the ultrasonic energy pulse continues to travel about the closed path.
 2. switch the output of the second transducer to the defect signal detector, and
 3. switch the output of the first transducer to the through-transmission signal detector, whereby the functions of the first and second transducers are reversed and the wheel is tested by passing an ultrasonic energy pulse about its periphery in a second, opposite direction.
 3. switch the output of the second transducer to the through-transmission signal detector in response to the elapsing of said time interval following the first through-transmission signal initiated by a through-transmission pulse from the second transducer, whereby the function of the first and second transducers are repetitiously alternated.
 3. having its top surface aligned with the top surfaces of the rail segments, and wherein a railroad wheel rolling along the thin vertical support rail is exposed to a test zone adjacent to the support rail closely juxtaposed to but not intruding into the normal path of the railroad wheel,
 3. The method of inspecting a body for defects in a curved peripheral surface thereof as described in claim 2 wherein the closed path curved peripheral surface comprises an ellipse.
 4. aligned with the inside gauge edge of the rail segments for supporting the running surface of a railroad wheel rolling thereover adjacent to its flange, D. an ultrasonic energy-transmitting medium positioned in the test zone adjacent to the thin vertical support rail for ultrasonic coupling with the running surface of a railroad wheel as it passes thereover, the ultrasonic energy-transmitting medium having an index of refraction substantially lower than the index of refraction of ultrasonic energy in the railroad wheel; E. a first transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to the top surface of the thin vertical support rail at an angle whereby low frequency ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted therein substantially tangent to the wheel surface, thereafter travelling about the periphery of the wheel: along a path near to and converging toward the curved surface and having a progressively increasing radius of curvature, and thereby migratIng convergingly toward said surface; F. a pulse generator connected to the first transducer for pulsing the first transducer to produce a low frequency ultrasonic energy pulse along its sonic axis; and, G. a defect signal detector connected to the first transducer for reception of the echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel, returning along the periphery of the wheel to the ultrasonic energy transmitting medium, and refracted out of the wheel to impinge on the first transducer the defect signal detector producing a defect alarm signal upon receipt of a defect echo pulse.
 4. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle whereby ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof along a path adjacent to and converging toward the surface with a progressively increasing radius of curvature; and D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium.
 5. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface; and D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium, wherein the ultrasonic energy pulse has a frequency of below 1, 000 kiloHertz, the ultrasonic energy pulse thereby initially penetrating to a substantial depth in the wheel, and thereafter gradually migrating toward the surface of the wheel as it travels thereabout.
 6. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 5, wherein the ultrasonic pulse has a frequency of 400 kiloHertz.
 7. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 4, wherein the method is performed with apparatus positioned adjacent to a wheel supporting surface and: E. rolling the wheel onto the apparatus to establish ultrasonic coupling therewith.
 8. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 7, wherein the wheel is a railroad wheel, and wherein the method is performed with apparatus positioned in a gap between two rail segments comprising from a portion of a railroad track.
 9. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 4, wherein monitoring the first ultrasonic transducer for echo pulses is performed for a predetermined time interval.
 10. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 4 and further comprising the steps of: E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer; and, F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel.
 11. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 10, and further comprising the step of: G. measuring the time interval during which the ultrasonic energy pulse passes about the periphery of the wheel, and indicating the wheel size therefrom.
 12. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially paralleL to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface, migrating convergingly toward said surface; D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium; E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer; F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel; G. measuring the strength of the through-transmission pulses received by the second transducer; and H. adjusting the gain of the amplified output of the first transducer as a function of the strength of the through transmission pulses received by the second transducer, wherein monitoring of the first transducer for defect echo pulses is more efficiently accomplished.
 13. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 12 wherein the gain of the amplified output of the first transducer is adjusted as a function of the strength of the largest through-transmission pulse received by the second transducer.
 14. The method of inspecting a wheel for defects in the peripheral surface thereof and further comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface; D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium; E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer; F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the fist transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel; G. pulsing the first ultrasonic transducer prior to coupling the wheel with the ultrasonic energy transmitting coupling medium, the pulse interval being larger than the time interval necessary for the pulse to travel about the periphery of the largest wheel to be tested; and H. inhibiting further pulsing of the first ultrasonic transducer upon receipt of the first through transmission pulse by the second transducer.
 15. The method of inspecting a wheel for defects and in the peripheral surface thereof comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface; D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium; E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer; F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel; G. subsequent to substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the first transducer, pulsing the second transducer to produce a second ultrasonic energy pulse delivered to the wheel along the sonic axis of the second transducer and refracted tangential to the surface of the wheel wherein the second ultrasonic energy pulse travels about the periphery of the wheel in a second opposite direction; and, H. monitoring for echo pulses received by the second ultrasonic transducer, the echo pulses comprising a portion of the second ultrasonic energy pulse reflected from a defect in the wheel.
 16. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 15 and further comprising the step of: I monitoring for through-transmission pulses received by the first transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel.
 17. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 16 and further comprising the step of: J. certifying that a complete test has been performed when through-transmission pulses have been received in both directions of travel by monitoring the second transducer for through transmission pulses and monitoring the first transducer for through-transmission pulses.
 18. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 15 wherein the second transducer is pulsed in synchronism with an attenuated through-transmission pulse delivered from the wheel to the second transducer.
 19. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface; D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium; E. positioning a second ultrasonic transducer in the coupling medium with the sonic axis of the second transducer substantially parallel to the plane of the wheel and inclined with respect to the plane tangent to the coupled zone at an angle substantially corresponding and opposite to the angle of the sonic axis of the first transducer wherein ultrasonic energy entering the coupled zone from within the wheel is refracted out of the wheel through the coupling medium to impinge upon the second transducer; F. monitoring for through-transmission pulses received by the second transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel by the first transducer and peripheral travel of the ultrasonic energy pulse about the periphery of the wheel; G. pulsing the second transducer subsequent to a predetermined time interval following pulsing of the first transducer, to produce a second ultrasonic energy pulse delivered to the wheel along the sonic axis of the second transducer and refracted therein substantially tangential to the surface of the wheel wherein the second ultrasonic energy pulse travels about the periphery of the wheel in a second opposite direction; and, H. monitoring for echo pulses received by the second ultrasonic transducer, the echo pulses comprising a portion of the second ultrasonic energy pulse reflected from a defect in the wheel.
 20. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 18 wherein said predetermined time interval is sufficient for substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the first transducer to occur.
 21. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 18 wherein the second transducer is pulsed in synchronism with the first attenuated through-transmission pulse occurring after the prEdetermined interval of time.
 22. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 16 wherein the method is performed by positioning the coupling medium adjacent to a wheel-supporting surface and further comprising the step of: J. rolling the wheel over the coupling medium to establish ultrasonic coupling therewith for a time interval dependent upon the speed of the wheel.
 23. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 22, wherein the first transducer is defined as the transducer facing the direction of approach of the wheel.
 24. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 16 and further comprising the step of: J. subsequent to substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the second transducer, repeating all of the above steps for as long as the wheel is coupled with the transducers.
 25. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 23 and further comprising the step of: A. subsequent to substantial attenuation of the ultrasonic energy pulse delivered to the wheel by the second transducer, repeating all of the above steps for as long as the wheel is coupled with the transducers.
 26. The method of inspecting a wheel for defects in the peripheral surface thereof comprising the steps of: A. coupling a zone of the outer peripheral surface of the wheel with an ultrasonic energy-transmitting coupling medium having an index of refraction of ultrasonic energy substantially lower than the index of refraction of ultrasonic energy of the wheel; B. positioning a first ultrasonic transducer in the coupling medium with the sonic axis of the transducer substantially parallel to the plane of the wheel and inclined with respect to a plane tangent to the coupled zone at an angle wherein ultrasonic energy delivered to the wheel along the sonic axis enters the wheel and is refracted substantially tangent to the wheel surface, migrating convergingly toward said surface; C. pulsing the first ultrasonic transducer to produce an ultrasonic energy pulse which travels along the sonic axis into the wheel, is refracted substantially tangent to the surface thereof, and thereafter travels in a first direction about the periphery thereof adjacent to the surface; D. monitoring the first ultrasonic transducer for received echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel and refracted to the first ultrasonic transducer by the coupling medium; and E. marking the wheel upon receipt of echo pulses at the first transducer.
 27. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 17, and further comprising the step of: K. marking the wheel upon certifying that a complete test has been performed.
 28. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 23 and further comprising the steps of: K. positioning a second ultrasonic energy-transmitting coupling medium adjacent to the wheel supporting surface and close to the first ultrasonic energy-transmitting coupling medium; L. positioning a third ultrasonic transducer in the second coupling medium in an orientation similar to the orientation of the first ultrasonic transducer in the first coupling medium; M. positioning a fourth transducer in the second coupling medium in an orientation similar to the orientation of the second ultrasonic transducer in the first coupling medium; N. performing the step of rolling the wheel over the first coupling medium to establish ultrasonic coupling therewith for a time interval dependent upon the speed of the wheel by rolling the wheel over the coupling medium at a sufficiently high speed that ultrasonic coupling is Destroyed prior to receipt of a through-transmission pulse by the first transducer, and thereafter; O. rolling the wheel over the second coupling medium to establish ultrasonic coupling therewith for a time interval dependent upon the speed of the wheel; P. upon establishing ultrasonic coupling with the second coupling medium, pulsing the fourth transducer to produce an ultrasonic energy pulse delivered to the wheel along the sonic axis of the fourth transducer and refracted tangential to the surface of the wheel wherein the ultrasonic energy pulse travels about the periphery of the wheel in a second opposite direction; and, Q. monitoring for echo pulses received by the fourth ultrasonic transducer, the echo pulses comprising a portion of the ultrasonic energy pulse reflected from a defect in the wheel.
 29. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 28 and further comprising the step of: R. monitoring for through-transmission pulses received by the third transducer, the reception of through-transmission pulses confirming delivery of an ultrasonic energy pulse into the wheel.
 30. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 28 wherein the first and third transducers are operated in parallel and the second and fourth transducers are operated in parallel.
 31. The method of inspecting a wheel for defects in the peripheral surface thereof as defined in claim 28 and further comprising the steps of: R. pulsing the fourth ultrasonic transducer prior to establishing coupling between the wheel and the second coupling medium, the pulse interval being larger than the time necessary for the pulse to travel about the periphery of the largest wheel to be tested; and S. inhibiting further pulsing of the fourth ultrasonic transducer upon receipt of the first through transmission pulse by the third transducer.
 32. Apparatus for testing railroad wheels comprising: A. a first rail segment comprising a portion of one rail of a railroad track; B. a second rail segment positioned a spaced apart distance from the first rail segment and aligned therewith to comprise a second portion of the same rail of a railroad track; and C. a thin vertical support rail
 33. Apparatus for testing railroad wheels as defined in claim 32 and further comprising: H. a second transducer positioned in the ultrasonic energy-transmitting medium with its sonic axis substantially parallel to the plane of the wheel and inclined with respect to the top surface of the rail at an angle substantially equal and opposed to the angle of inclination of the sonic axis of the first transducer; and I. a through-transmission signal detector connected to the second transducer for detecting through-transmission pulses comprising a portion of the ultrasonic energy pulse produced by the first transducer, traveling about the periphery of the wheel in a first direction returning to the coupling medium, and refracted out of the wheel to impinge upon the second transducer.
 34. Apparatus for testing railroad wheels as defined in claim 33 wherein the pulse generator is a synchronizing pulse generator set at a pulse interval greater than the time necessary for an ultrasonic energy pulse to travel about the periphery of the largest wheel to be tested, and wherein the output of the through-transmission signal detector controls the output of the synchronizing pulse generator to inhibit further pulsing upon receipt of the first through-transmission pulse, thereby permitting only one ultrasonic energy pulse to be delivered to the wheel.
 35. Apparatus for testing railroad wheels as defined in claim 34 and further comprising: J. a time delay connected to the output of the through-transmission signal detector and initiated by the first through-transmission signal to provide a time interval following the first through-transmission pulse selected to permit substantial attenuation of the first ultrasonic energy pulse in the wheel to occur, and connected to provide an output signal following the time interval at a time delay output terminal; K. a plurality of switches responsive to the output signal of the time delay and connected to:
 36. Apparatus for testing railroad wheels as defined in claim 35 wherein the switches are connected to
 37. Apparatus for testing railroad wheels as defined in claim 35 and further comprising: L. a third transducer positioned in the ultrasonic energy-transmitting medium in an orientatIon corresponding to the orientation of the first transducer, longitudinally spaced apart therefrom, and connected in parallel therewith; M. a fourth transducer positioned in the ultrasonic coupling medium adjacent to the third transducer in an orientation similar to the second transducer, longitudinally spaced apart therefrom, and connected in parallel therewith, whereby if the wheel has passed by the first and second transducers toward the third and fourth transducers prior to reception of a through-transmission pulse of a second, opposite direction ultrasonic energy pulse, the output of the synchronizing pulse generator is not inhibited until a second ultrasonic energy pulse is delivered to the wheel by the fourth transducer and a through-transmission pulse is received at the third transducer.
 38. Apparatus for testing railroad wheels as defined in claim 37 wherein the ultrasonic energy-transmitting medium has a first portion having the first and second transducers positioned therein and a second portion having the third and fourth transducers positioned therein, and wherein the second portion is positioned in a second test zone.
 39. Apparatus for testing railroad wheels as defined in claim 35 and further comprising: L. means connecting the output of the through-transmission signal detector to the synchronizing pulse generator for synchronizing the output thereof with through-transmission signals, whereby the second transducer is pulsed in synchronism with the attenuating through-transmission pulses.
 40. Apparatus for testing railroad wheels as defined in claim 36 wherein the first and second transducers have a resonant frequency less than 1,000 kiloHertz.
 41. Apparatus for testing railroad wheels as defined in claim 36 wherein the first and second transducers have a resonant frequency of 400 kiloHertz.
 42. Apparatus for testing railroad wheels as defined in claim 35 and further comprising: L. two wheel sensors positioned flanking the test zone connected to provide an output signal indicating the direction from which a railroad wheel is approaching the test zone.
 43. Apparatus for testing railroad wheels as defined in claim 42 and further comprising: K. a direction control switch interposed between the synchronizing pulse generator and the inputs to the first and second transducers, the direction control switch connecting the synchronizing pulse generator to first pulse the transducer which is the first to have its sonic axis coupled with the wheel in response to the output of the wheel sensing switches.
 44. Apparatus for testing railroad wheels as defined in claim 43 wherein the sonic axes of the first and second transducers cross below the surface of the thin vertical support rail, and wherein the transducer facing the direction of approach of the wheel is first pulsed.
 45. Apparatus for testing railroad wheels as defined in claim 35 and further comprising: L. a pressurized paint spray having an output nozzle directed toward the wheel being tested and a valve controlling the release of paint therefrom; and M. means for operating the valve responsive to a defect alarm signal, whereby a wheel having a defect is marked with paint. 